Field of the Invention
The present invention relates to an organic light emitting device. More particularly, the present invention relates to a white organic light emitting device including various emission layers with improved luminous efficiency, an increased color viewing angle, and low power consumption.
Discussion of the Related Art
Image display devices have become a core technology in the information communication era. The devices embody various kinds of information on a screen and have been developed such that the image display devices are thin, light, portable and have high performance. An organic light emitting device (OLED) that controls a luminance amount of an organic emission layer to display an image has been spotlighted as a flat panel display device having smaller weight and volume than a cathode ray tube (CRT).
An organic light emitting device, which is a self-emissive device having a thin emission layer disposed between two electrodes, may be configured to be thin as paper. Specifically, the organic light emitting device includes an anode, a hole injection layer (HIL), a hole transport layer (HTL), an emission layer, an electron transport layer (ETL), an electron injection layer (EIL), and a cathode.
In recent years, active research has been conducted into a white organic light emitting device having a multi-layer structure (two stacks or more) in order to further improve luminous efficiency.
That is, two or three stacks are provided and one emission layer is provided per stack to embody a white light emitting device. This white light emitting device may emit light having a white wavelength. When the white light emitting device is applied to a panel, however, luminance is low and power consumption is high due to a critical value of luminous efficiency provided by each emission layer.
Alternatively, two or three stacks can be provided and three emission layers are provided per stack to embody a white spectrum. When this white light emitting device is applied to a panel, however, luminance is still low and power consumption is high.
FIG. 1 is a view showing the structure of a related art two-stack white organic light emitting device, FIG. 2 is a view showing the structure of another related art two-stack white organic light emitting device, and FIG. 3 is a view showing the structure of a related art three-stack white organic light emitting device.
As shown in FIG. 1, the related art white organic light emitting device has a structure in which a first stack 3, a charge generation layer 5, and a second stack 4 are stacked between an anode 1 and a cathode 2.
The first stack 3 includes a hole transport layer 3a and a first emission layer 3bThe second stack 4 includes a second emission layer 4a and an electron transport layer 4b. The first emission layer 3b is a blue (B) emission layer and the second emission layer 4a is a yellow-green (YG) emission layer.
As shown in FIG. 2, the related art white organic light emitting device has a structure in which a first stack 3, a charge generation layer 5, and a second stack 4 are stacked between an anode 1 and a cathode 2. The first stack 3 includes a hole transport layer 3a and three emission layers 3c. The second stack 4 also includes three emission layers 4c and an electron transport layer 4b. The three emission layers 3c and 4c include blue (B), green (G), and red (R) emission layers.
As shown in FIG. 3, the related art white organic light emitting device has a structure in which a first stack 3, a first charge generation layer 5, a second stack 4, a second charge generation layer 6, and a third stack 7 are stacked between an anode 1 and a cathode 2. The first stack 3 includes a hole transport layer 3a and a first emission layer 3b. The second stack 4 includes a second emission layer. The third stack 7 includes a third emission layer 7b and an electron transport layer 7a. The first emission layer 3b is a blue emission layer, the second emission layer is a green emission layer, and the third emission layer 7b is a red emission layer.
In the related art white organic light emitting devices, each charge generation layer is formed between the respective stacks to adjust a charge balance between the respective stacks.
However, the related art white organic light emitting devices have the following problems.
The related art white organic light emitting devices shown in FIGS. 1 and 3 have similar characteristics. However, the related art white organic light emitting device shown in FIG. 1 has a smaller number of layers and a smaller overall thickness than the related art white organic light emitting device shown in FIG. 3. Consequently, the related art white organic light emitting device shown in FIG. 1 may have lower drive voltage and emit light having a white wavelength. Because it is necessary to cover three peaks using two peaks, however, in the related art white organic light emitting device shown in FIG. 1, luminance is low and power consumption is high due to a critical value of luminous efficiency provided by each emission layer when the white organic light emitting device is applied to a panel. In addition, in the related art white organic light emitting device shown in FIG. 1, a color viewing angle is limited due to each layer and an optical path based on a thickness corresponding thereto.
In the related art white organic light emitting device shown in FIG. 2, each stack has low luminous efficiency and a short life span. Although the stacks are stacked, a color viewing angle is greatly limited and there are many color shifts.